Re: [PATCH] omapdss: Add new panel driver for Topolly td028ttec1 LCD.

On 10/11/2013 10:59 AM, Belisko Marek wrote:

Hi Tomi,

On Fri, Oct 11, 2013 at 10:17 AM, Tomi Valkeinen [off-list ref] wrote:

quoted

On 11/10/13 10:42, Dr. H. Nikolaus Schaller wrote:

quoted

I am not sure if there is a SPI driver for a McBSP port [1]? And to make that
work (reliably) and tested it might need a lot of work for us. At least I think
such a change (e.g. setting up clock polarity etc.) is not done in some minutes.
And the only feedback we have from the panel is "does not work"/"works". I.e.
if we are not lucky that it works immediately we have no real means to debug.

IMHO it also gives more flexibility to board designers to choose GPIOs instead
of enforcing some SPI interface by the driver (and encapsulate this arguable
protocol in the driver). Maybe some board has 3 spare GPIOs but neither
McBSPs nor McSPIs available.

This has been an interesting thread, I've learnt a lot =).

I still think the panel driver should not handle this, but there should
be a separate spi bitbang driver for it.

I understand you're not enthusiastic going that way, as the current
version works for you. However, when using DT, we need to think how to
represent the hardware in the device tree data, and it has to be right
from the beginning.

That's why I won't allow representing this panel as having 4 gpios in
the DT data, because that is not correct. The panel has 3 pins. But
then, the panel does allow reading, which could be implemented using 4
gpios as you have done. This data should be in the spi-bitbang data, and
the panel should just use the standard SPI framework.

I disagree. There are different drivers which pass in platform data
gpios (encoder-tfp410.c or encoder-tpd12s015.c)
and those must be covered by DT then. I cannot see problem why to have
for td028 panel 3 or 4 gpios defined in DT.

The problem is not representing it in the devicetree, but representing it
correctly. This is a SPI slave device, hence it should be presented in the
devicetree as a SPI slave device and not as a platform device with 4 GPIOs.

- Lars